The present invention relates to a scroll type fluid displacement apparatus, and more particularly, to a tool for manufacturing the scroll of a scroll type fluid displacement apparatus.
Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 (Cruex) discloses a fluid displacement apparatus including two scrolls, each having a circular end plate and a spiroidal or involute spiral element. Both scrolls are maintained at an angular and radial offset so that the spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the scrolls shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pockets changes. Since the volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion, scroll type fluid displacement apparatus are applicable to compress, expand or pump fluids.
FIG. 1 of the drawings illustrates a basic design of a scroll 1 suitable for use in a scroll type fluid displacement apparatus. Scroll 1 includes a circular end plate 2 and a wrap or involute spiral element 3 affixed to or extending from one end surface of end plate 2. A scroll type fluid displacement apparatus includes a pair of such scrolls, both of which are maintained at an angular and radial offset so that they interfit to form a plurality of line and axial contacts to define at least one pair of sealed off fluid pockets. In such apparatus, each sealed off fluid pocket is defined by the line contacts between interfitting spiral elements and the axial contacts between the axial end surface of each spiral element and the inner end surface of the end plate of the other scroll. The volume of the pocket is thereby defined by the line contacts and the axial contacts.
The scroll is generally formed from single pieces of metal by a machining process such as milling. However, a milling machine process consumes a great deal of time and energy; it also produces large quantities of waste metal. If the scroll is formed by casting or forging, and if the axial dimensions of the spiral element must be made relatively long to obtain a large volume or high capacity, the draft angle of the mold must be made large. After forming in such a mold, a large amount of machining of the spiral element is required to obtain uniform wall thickness; as a result, relatively large quantities of waste metal are produced and a great deal of time and energy are expended. Furthermore, this manufacturing process makes it difficult to attain high accuracy of the wall dimensions of the spiral element.
In order to avoid these disadvantages in single piece construction of a scroll, U.S. Pat. No. 3,994,635 (McCullough) discloses a scroll consisting of two pieces. The scroll is formed of a separate end plate and spiral element. The end plate has an involute configured groove on one side surface and the separate spiral element is seated in the groove. However, in this construction, the process of seating the spiral element in the groove is intricate. Also, after seating the spiral element, finishing the surface of the end plate and the spiral element is intricate and difficult. Finally, in comparison with single piece scrolls, the reliability of two piece scrolls is inferior.